Light emitting device and camera having the same

ABSTRACT

A light emitting device that is capable of changing the illumination angle in the transverse direction while efficiently utilizing energy from a light source. An emission unit includes at least an arc tube. A pair of reflecting means are arranged in a longitudinal direction of the arc tube so as to reflect luminous fluxes emitted from the arc tube in a direction which varies according to the distance between the emission unit and each of the reflecting means.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/941,334,filed Aug. 29, 2001 now U.S. Pat. No. 6,741,014.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a light emitting device capable of changing anillumination range and a camera having the same.

2. Description of the Related Art

Conventionally, a variety of illuminating devices for use in aphotographing apparatus such as a camera have been proposed in order toefficiently converge luminous fluxes, which are emitted from a lightsource in various directions, within a required illumination angle ofview.

Particularly in recent years, the convergence efficiency have beenimproved and the size of a photographing apparatus has been reduced byproviding an optical member that performs total reflection on a prism, alight guide, and the like in place of a Fresnel lens, which isconventionally disposed in front of a light source.

In recent years, a photographing apparatus such as a camera has beenreduced in size and weight whereas the zooming magnification of a takinglens has been increasing. Generally, a full aperture f-number of thetaking lens tends to gradually increase with the reduction in size ofthe photographing apparatus and the increase in the magnification. If apicture is taken without using an auxiliary light source, an image onthe picture is unexpectedly blurred due to the motion of thephotographer's hand or the motion of a subject, or a failed picture isproduced due to underexposure. To address this problem, an illuminatingdevice serving as an auxiliary light source is usually built in thephotographing apparatus.

Under the circumstances, the frequency with which the illuminatingdevice is used is increased to a large extent, and the quantity ofemitted light required for one photography is increased. Thus, theillumination range is usually fixed correspondingly to the wide-anglephotography, and an undesired range is illuminated in thetelephotography. It is therefore disadvantageous to use an illuminatingdevice with a fixed wide illumination range since a large amount ofenergy is lost.

Accordingly, a variety of illuminating devices have been proposed whichare capable of changing the illumination range so as to illuminate onlya range corresponding to a shooting angle of view to thus save power. Inparticular, some illuminating devices have been proposed which improvethe luminous efficiency by total reflection.

For example, an illuminating device proposed in Japanese Laid-OpenPatent Publication No. 4-138439 (Kokai) by the assignee of the presentinvention has a convergent optical system arranged at a front portion ofthe illuminating device and comprised of an optical prism having twoupper and lower entrance surfaces having a positive refracting power andwhich luminous fluxes emitted mainly from a light source laterally withrespect to an exit optical axis enter, two upper and lower totalreflection surfaces upon which the luminous fluxes are totallyreflected, and exit surfaces through which the totally reflected fluxesare emitted toward a subject. In this convergent optical system, thepositions of the optical prism and the light source are relativelychanged to cause the luminous fluxes to be reflected by or transmittedthrough the total reflection surfaces to thereby change the illuminationrange.

In an illuminating device proposed in Japanese Laid-Open PatentPublication (Kokai) No. 8-262538, an optical prism is divided into aplurality of parts, and the optical prism disposed vertically is rotatedto change the illumination range.

However, the illuminating devices disclosed in the above publicationsprovide a relatively easy convergence and diffusion control of directingthe luminous fluxes in a diametrical direction of a cylindricaldischarge arc tube as the light source, i.e. in a direction (verticaldirection) orthogonal to the longitudinal direction of the light source(transverse direction with respect to the axis of illumination light),but do not provide a convergence diffusion control of directing theluminous fluxes in the longitudinal direction of the light source(transverse direction with respect to the axis of illumination light).Therefore, the illumination range cannot always be controlled in anideal manner because the illumination range can be controlled only inthe longitudinal direction.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a lightemitting device that can be reduced in size as a whole, and that iscapable of efficiently utilizing energy from a light source and changingthe illumination angle in the transverse direction, and a cameraincorporating the light emitting device.

To attain the above object, the present invention provides a lightemitting device comprising an emission unit including at least an arctube, and a pair of reflecting means arranged in a longitudinaldirection of the arc tube, for reflecting luminous fluxes emitted fromthe arc tube in a direction which varies according to a distance betweenthe emission unit and each of the reflecting means.

BRIEF DESCRIPTION OF THE DRAWINGS

The nature of this invention, as well as other objects and advantagesthereof, will be explained in the following with reference to theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures and wherein:

FIG. 1 is a horizontal longitudinal sectional view showing anilluminating device as a light emitting device according to a firstembodiment of the present invention, which is in a narrow illuminationrange position, taken along the axis of a discharge tube;

FIG. 2 is a horizontal longitudinal sectional view showing theilluminating device, which is in a wide illumination range position,taken along the axis of the discharge tube;

FIG. 3 is a vertical longitudinal sectional view showing theilluminating device, which is in a narrow illumination range position,taken in a diametric direction of the discharge tube;

FIG. 4 is a vertical longitudinal sectional view showing theilluminating device, which is in a wide illumination range position,taken in the diametric direction of the discharge tube;

FIG. 5 is a perspective view showing essential parts of an opticalsystem of the illuminating device;

FIG. 6 is a perspective view showing a camera to which the illuminatingdevice according to the first embodiment is applied;

FIG. 7 is a diagram showing light distribution characteristics, thediagram being useful in explaining the illumination range of theilluminating device according to the first embodiment;

FIG. 8 is a horizontal longitudinal sectional view showing anilluminating device as a light emitting device according to a secondembodiment of the present invention, which is in a narrow illuminationrange position, taken along the axis of a discharge tube;

FIG. 9 is a horizontal longitudinal sectional view showing theilluminating device according to the second embodiment, which is in awide illumination range position, taken along the axis of the dischargetube;

FIG. 10 is a vertical longitudinal sectional view showing theilluminating device according to the second embodiment, which is in anarrow illumination range position, taken in the diametric direction ofthe discharge tube;

FIG. 11 is a vertical longitudinal sectional view showing theilluminating device according to the second embodiment, which is in awide illumination range position, taken in the diametric direction ofthe discharge tube;

FIG. 12 is a perspective view showing essential parts of an opticalsystem of the illuminating device according to the first embodiment;

FIG. 13 is a diagram showing light distribution characteristics, thediagram being useful in explaining the illumination range of theilluminating device according to the second embodiment;

FIG. 14 is a horizontal longitudinal sectional view showing anilluminating device as a light emitting device according to a thirdembodiment of the present invention, which is in a narrow illuminationrange position, taken along the axis of a discharge tube;

FIG. 15 is a horizontal longitudinal sectional view showing theilluminating device according to the third embodiment, which is in awide illumination range position, taken along the axis of the dischargetube;

FIG. 16 is a horizontal longitudinal sectional view showing theilluminating device according to the third embodiment, which is in anarrow illumination range position, taken in the diametric direction ofthe discharge tube; and

FIG. 17 is a horizontal longitudinal sectional view showing theilluminating device according to the third embodiment, which is in awide illumination range position, taken in the diametric direction ofthe discharge tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference tothe drawings showing embodiments thereof.

FIGS. 1 to 6 show an illuminating device as a light emitting deviceaccording to a first embodiment of the present invention. FIGS. 1 and 2are horizontal longitudinal sectional views showing essential parts ofan optical system of the illuminating device, whereas FIGS. 3 and 4 arevertical longitudinal sectional views showing essential parts of theoptical system of the illuminating device. FIG. 5 is a perspective viewshowing only the principal optical system of the illuminating device,and FIG. 6 is a perspective view showing a camera having theilluminating device. FIGS. 1 to 4 also show the traces of typical lightrays emitted from a light source.

First, there will be described the whole arrangement of the camerahaving the illuminating device. As shown in FIG. 6, the illuminatingdevice 1 is retractably disposed in an upper section of a camera body11, and is designed to project from a lateral side of the camera body 11when the camera is used.

In FIG. 6, reference numeral 12 denotes a lens barrel that holds ataking lens; 13, a shutter release button; 14, a telephoto zoomingbutton; 15, a wide-angle zooming button; 16, an operating button forchanging the mode of the camera; 17, a liquid crystal display window forgiving information on the operation of the camera to a user; 18, a lightreceiving window of a photometer that measures the brightness ofexternal light; and 19, an objective window of a finder. It should benoted that the camera having the illuminating device according to thepresent invention should not necessarily be limited to a camera havingthis arrangement.

Referring next to FIG. 5, there will be described the components of theilluminating device relating to the optical characteristics. In FIG. 5,reference numeral 2 denotes a discharge arc tube (xenon tube), which isshaped like a straight and long cylinder and emits luminous fluxes. Thedischarge arc tube 2 is arranged so as to extend in a transversedirection of the illuminating device 1. Reference numeral 3 denotes areflection umbrella that reflects components, which are emitted backwardin a light emitting direction, among the luminous fluxes emitted fromthe discharge arc tube 2 forward in the light emitting direction. Theinner surface of the reflection umbrella 3 is made of a metallicmaterial such as bright aluminum having a high reflectance. It shouldnoted that a metal having a high reflectance may be deposited on theinner surface of the reflection umbrella 3.

Reference numeral 4 denotes a light-permeable light guide member thatdivides the luminous fluxes emitted from the discharge arc tube 2 intoluminous fluxes in some optical path regions, emits the luminous fluxesin the respective regions from an exit surface, and then causes theemitted luminous fluxes to intersect at predetermined intervals tochange the light distribution characteristics so that the luminousfluxes can be distributed in a predetermined range.

Reference numeral 5 denotes a light-permeable optical member thatreceives the luminous fluxes emitted from the light-permeable lightguide member 4 to change the light distribution characteristics so thatthe luminous fluxes can be distributed in a required predeterminedrange. A plurality of cylindrical lenses 5 a, 5 b, 5 b′ capable ofrefracting light vertically are formed in parallel juxtaposition in thevertical direction on a light exit surface of the optical member 5.Vertically extending prism sections (condensing sections) 5 h, 5 h′having total reflection inner surfaces are formed at the right and leftside edges of the light-permeable optical member 5.

The discharge arc tube 2, the reflection umbrella 3 and the light guidemember 4 are integrally held in a holding case, not shown, to constitutean emission unit. The emission unit is movable relative to the opticalmember 5 which is fixed to an outer surface of the illuminating device 1according to the power changing operation of the lens barrel 12. Thiscontinuously changes the degree of convergence of illumination light. Itshould be noted that the light guide member 4 and the optical member 5are preferably made of a resin material for optical use with a highlight transmittance such as acryl resin or a glass material.

If a “strobe auto mode” is set in the camera that is constructed asdescribed above, a central processing unit, not shown, determineswhether to cause the illuminating device 1 to emit light according tothe brightness of external light measured by the photometer, not shown,and the sensitivity of a loaded film after a user pressed the shutterrelease button 13.

Upon determining that it is necessary to cause the illuminating device 1to emit light, the central processing unit outputs a light emissioninstruction to cause the discharge arc tube 2 to emit light via atrigger lead line, not shown, attached to the reflection umbrella 3.Luminous fluxes emitted in an illuminating direction among illuminatingluminous fluxes emitted by the discharge arc tube 2 are directlytransmitted through the light guide member 4 and the optical member 5,which are disposed in front of the discharge arc tube 2, to change thelight distribution characteristics so that the luminous fluxes aredistributed in a predetermined range. On the other hand, luminous fluxesemitted in an opposite direction to the illuminating direction among theilluminating luminous fluxes emitted by the discharge arc tube 2 aretransmitted through the light guide member 4 and the optical member 5,which are disposed in front of the discharge arc tube 2, via thereflection umbrella 3 to change the light distribution characteristicsso that the luminous fluxes are distributed in a predetermined range.The luminous fluxes are then radiated upon a subject.

The light distribution characteristics are changed only by the relativemovement of the emission unit (i.e. the light guide member 4) and theoptical member 5 along the axis of illumination light (i.e. the movementof the emission unit).

According to the present embodiment, if the taking lens of the camera isa zoom lens, the relative positions of the emission unit and the opticalmember 5 along the axis of illumination light are varied according tothe focal length of the zoom lens. This enables simultaneous adjustmentof the light distribution characteristics in both the transverse andvertical directions according to a required illumination range of thetaking lens.

There will now be described the method of setting the optimum opticalarrangement for changing the illumination range with reference to FIGS.1 to 4.

Referring first to FIGS. 3 and 4, the basic principle of changing theillumination range in the diametric direction of the discharge tube(vertical direction) in the illuminating device 1 will be described. InFIGS. 3 and 4, elements and parts similar to those described withreference to FIGS. 5 are denoted by the same reference numerals.

FIG. 3 shows a state in which the optical unit and the optical member 5are arranged at the maximum interval. FIG. 4 shows a state in which theoptical unit and the optical member 5 are arranged at the minimuminterval. FIGS. 3 and 4 also show optical paths of typical light raysemitted from the center of the inner diameter of the discharge arc tube2.

The illuminating device 1 described here is capable of continuouslychanging the illumination range while maintaining uniform longitudinallight distribution characteristics, and has an opening that is designedto have the minimum height.

FIGS. 3 and 4 show the inner and outer diameters of a glass portion ofthe discharge arc tube 2. A discharge arc tube for use in this kind ofilluminating device usually emits light from the whole inner diameter soas to improve the efficiency. Thus, it may be considered that light isuniformly emitted from emission points over the whole inner diameter ofthe discharge arc tube 2. To simplify the explanation, however, lightrays emitted from the center of the light source are considered as beingtypical light rays, and thus, the figures only show the typical lightrays emitted from the center of the light source. The actual lightdistribution characteristics are changed such that the entiredistribution of light becomes slightly wider due to luminous fluxesemitted from the periphery of the discharge arc tube 2 as well as thetypical light rays shown in the figures, but the tendencies of the lightdistribution characteristics are substantially the same. Therefore, thefollowing description will be made based on the typical light rays.

First, there will be sequentially described the characteristics of theilluminating optical system that is constructed as described above. Theinner surface of the reflection umbrella 3 is semicylindrical andsubstantially concentric with the outer peripheral surface of thedischarge arc tube 2. This enables light reflected by the reflectionumbrella 3 to return to the vicinity of the center of the light sourceand prevents the light from badly affected by the refraction on theglass of the discharge arc tube 2. Moreover, this structure andarrangement of the reflection umbrella 3 is convenient since it enablesthe light reflected by the reflection umbrella 3 to be handled asemitted light that is substantially equivalent to direct light from thelight source, and enables the reduction in size of the downstreamoptical system as a whole.

The reason why the reflection umbrella 3 is just semicylindrical is thatif it is smaller, the light guide member 4 must be increased in size inorder to converge light emitted toward the side and that if it islarger, the efficiency is lowered due to the increase in luminous fluxesinside the reflection umbrella 3.

According to the present embodiment, the light guide member 4 isconstructed as described below. Cylindrical lenses providing a positiverefracting power to both an entrance surface 4 a and an exit surface 4 bare formed at the center of the light guide member 4. Therefore, asshown in FIG. 3, a luminous flux emitted from the center of thedischarge arc tube 2 is converged at a position P along a straight lineextending vertically, i.e. perpendicularly to the plane of the figure.

In upper and lower sections of the light guide member 4, the luminousflux emitted from the center of the discharge arc tube 2 is refractedupon entrance surfaces 4 c, 4 c′ and is then reflected by reflectionsurfaces 4 d, 4 d′ to be emitted from exit surfaces 4 e, 4 e′. Among therays of light reflected by the reflection surfaces 4 d, 4 d′, the raysof light reflected at a front portion of the reflection surfaces 4 d, 4d′ are guided in such a direction as to get closer to the center of theexit optical axis, the rays of light reflected at the central portionare guided in substantially parallel to the exit optical axis, and therays of light reflected at portions close to the light source are guidedin such a direction as to go farther away from the center of the exitoptical axis. The reflected luminous fluxes are distributed uniformly.

On the other hand, the three cylindrical lenses 5 a, 5 b, 5 b′ having apositive refracting power are formed side by side in the verticaldirection on the exit surface of the optical member 5, as describedpreviously. More specifically, as shown in the figures, the threecylindrical lenses 5 a, 5 b, 5 b′ are formed at locations correspondingto the following three areas: an area of convergence by the cylindricallens formed at the center of the light guide member 4 and two upper andlower areas of convergence by total reflection surfaces.

The forms of the respective surfaces of the light guide member 4 willnow be described in further detail. The cylindrical lenses formed on theentrance surface 4 a and the exit surface 4 b that control angularcomponents close to the exit optical axis by direct refraction areaspherical lenses whose shapes are determined so that a luminous fluxemitted from the center of the light source can be made parallel to theexit optical axis by the entrance surface 4 a and then converged at thepoint P by the exit surface 4 b.

This is intended to make it easier to set the optimum shape of the exitsurface 4 b by making the luminous flux refracted upon the entrancesurface 4 a parallel to the exit optical axis. However, the shapes ofthe cylindrical lenses should not necessarily be limited to such shapesas to make the luminous flux emitted from the center of the light sourceparallel to the exit optical axis by the entrance surface 4 a. There isno particular limitation as to how to provide the lens surfaces withrefracting power insofar as the luminous flux can be transmitted throughthe light guide member 4 and converged in the vicinity of the point P sothat the maximum exit angle and the minimum exit angle can be equal topredetermined angles. Therefore, the use of aspherical lenses is not anessential condition; for example, a combination of a spherical lens anda cylindrical lens may be adopted.

There will now be described the shapes of the entrance surfaces 4 c, 4c′ that guide the incident light to the total reflection surfaces 4 d, 4d′ of the light guide member 4. The entrance surfaces 4 c, 4 c′ arepreferably parallel to the optical axis so as to minimize the size ofthe light guide member 4. More specifically, the luminous flux flowingin a different direction from the exit optical axis is refracted once bythe entrance surfaces 4 c, 4 c′. As the angle of the entrance surfacesis smaller, the effect of the refraction increases so that the incidentlight can be guided due to the refraction in such a direction as to gofarther from the optical axis. This reduces the total length of theoptical prism.

Actually, however, the inclination of the entrance surfaces 4 c, 4 c′substantially depends on the conditions under which the light guidemember 4 is formed. As the angle of the entrance surfaces 4 c, 4 c′ issmaller, the actual forming conditions become more strict. Preferably,the maximum value Φ of the angle of the entrance surfaces is set withinthe following range irrespective of whether the entrance surfaces 4 c, 4c′ are flat or curved:0≦Φ<2°  (1)

It seems to be difficult to set the angle within this range, but it isactually possible to set the angle within this range since the entrancesurfaces 4 c, 4 c′ are positioned at a short interval and they are flatand smooth. By determining the inclination of the entrance surfaces 4 c,4 c′ in this manner, it is possible to minimize the height of theopening without deteriorating the efficiency.

There will now be described the shape of the reflection surfaces 4 d, 4d′. As stated previously, the shape of the reflection surfaces 4 d, 4 d′is determined such that among the rays of light reflected by thereflection surfaces 4 d, 4 d′, the rays of light reflected at the frontportion of the reflection surfaces 4 d, 4 d′ are guided in such adirection as to get closer to the center of the exit optical axis, therays of light reflected at the central portion are guided insubstantially parallel to the exit optical axis, and the rays of lightreflected at portions close to the light source are guided in such adirection as to go farther away from the center of the exit optical axisand that the reflected luminous fluxes are distributed uniformly.

As is the case with the entrance surface 4 a and the exit surface 4 bthat control angular components close to the exit optical axis by directrefraction, the shape of the reflection surfaces 4 d, 4 d′ is preferablydetermined so that the rays of light can be converged at one point. Thisincreases the size of the light guide member 4 and the space requiredfor changing the illumination range. This results in an increase in thesize of the optical system as a whole in the illuminating device 1.Without increasing the size of the optical system, it is difficult tomake the vertical illumination angles coincide and make the verticallight distribution characteristics uniform.

Therefore, according to the present embodiment, the shape of reflectionsurfaces 4 d, 4 d′ is determined in such a manner as to achievesubstantially the same effects as the above-mentioned one-pointconvergence. This makes it possible to achieve substantially the sameeffects as the entrance surface 4 a and the exit surface 4 b whilekeeping the light guide member 4 small in size.

On the other hand, although not illustrated, the luminous fluxes goingbackward along the exit optical axis among the luminous fluxes emittedfrom the discharge arc tube 2 are reflected by the reflection umbrella 3and then enter again upon the discharge arc tube 2 to be guided forwardalong the exit optical axis via substantially the center of thedischarge arc tube 2, because the reflection umbrella 3 is formedconcentrically with the discharge arc tube 2. After returning to thecenter of the light source, the luminous fluxes are guided in the samemanner as described above.

There will now be described the shape of the optical member 5. Theoptical member 5 is a flat member that can also be used as an outsidemember of the illuminating device 1 or the camera. Three lenses havingpositive refracting power are formed on the light exit surface of theoptical member 5.

The lenses have such shapes as to change the degree of conversion oflight emitted from a central area of convergence by the cylindrical lenswith a positive refracting power and two upper and lower areas ofconvergence by total reflection surfaces as stated above with referenceto the light guide member, at respective predetermined rates. Thedistribution of light is changed in the same manner in the three areasby adjusting the distance between the light guide member 4 and theoptical member 5.

As shown in FIG. 3, the central lens among the three lenses is anaspherical lens configured such that the luminous flux emitted from thepoint P is refracted by the exit surface 5 a of the optical member 5into light rays substantially parallel to the exit optical axis. Theupper and lower two lenses are formed as correction surfaces asdescribed below since the luminous fluxes reflected by the totalreflection surfaces 4 d, 4 d′ of the light guide member 4 do notconverge at one point.

More specifically, the surfaces of the upper and lower lenses are shapedso that the upper half and the lower half of each lens have differentcharacteristics so as to make all the luminous fluxes transmittedthrough the exit surface parallel to the exit optical axis in the statein which the light guide member 4 and the optical member 5 are locatedat a predetermined interval.

This will now be described in further detail. In each lens, a partoutside a component parallel to the exit optical axis in proximity tothe center among all components of reflected light is comprised of alens surface having a low refracting power, and a part inside thecomponent is comprised of a lens surface having a high refracting power.

This arrangement achieves the maximum convergence in the verticaldirection as shown in FIG. 3 in the state in which the light guidemember 4 and the optical member 5 are located at a predeterminedinterval. In the maximum convergence, controlling the light by utilizingthe opening of the optical member 5 to the utmost limit is an importantcondition for realizing an illuminating device that emits a largequantity of light. A small-sized illumination optical system with a highefficiency can be realized by satisfying this condition.

On the other hand, to achieve a light distribution characteristic inwhich the light is distributed in the widest range in the verticaldirection, the light guide member 4 and the optical member 5 arepositioned at the minimum interval as shown in FIG. 4. In this position,the positions of maximum convergence areas formed in front of the exitsurfaces 4 b, 4 e, 4 e′ substantially correspond to positions of therespective exit optical axes of the lenses formed at the exit side ofthe optical member 5, i.e. the centers of the lenses as shown in thetrace drawing showing the rays of light.

By making the maximum convergence areas obtained by the light guidemember 4 substantially correspond to areas that are not greatly affectedby the refracting power of the lenses in proximity to the centers of theoptical axes of the lenses formed at the exit side of the optical memberas stated above, it is possible to radiate the illuminating luminousfluxes on a subject with a light distribution characteristic that issubstantially equivalent to the light distribution characteristicobtained in the case where the light is converged by the light guidemember 4 alone.

More specifically, by arranging the optical system as stated above andproperly setting a predetermined convergence by the light guide member 4and the thickness of the optical member 5, it is possible to achieve auniform light distribution characteristic with the widest illuminationrange, with a small loss, that corresponds to a required illuminationarea of the wide-angel taking lens. To achieve such a characteristic,the parts of the light guide member 4 are preferably shaped so that theconvergences in the respective parts of the light guide member 4 cansubstantially correspond to one another.

Incidentally, the lens surface of the optical member 5 is formed at theexit side according to the present embodiment, and this is advantageousfor reducing the size of the optical system of the illuminating device.Specifically, as the interval between the light source and a lightcontrol surface increases, the degree of convergence by refraction ishigher. Thus, by arranging the light control plane at the farthestlocation in the optical system, the optical system of the illuminatingdevice can be reduced in size along the exit optical axis.

Moreover, by arranging the optical system in the intermediate statebetween the state in FIG. 3 and the state in FIG. 4, it is possible tocontinuously change the effect of the refracting power of thecylindrical lenses 5 a, 5 b, 5 b′ by moving the same, i.e. changing thedistance thereof relative to the optical system. It is thereforepossible to change the light distribution characteristics according tothe distance. By regulating the relative distance between the opticalsystem and the cylindrical lenses, it is possible to change the lightdistribution characteristics continuously and uniformly.

Thus, it is possible to continuously change the light distributioncharacteristic in the vertical direction according to the change in therelative positions of the light guide member 4 and the optical member 5along the exit optical axis.

Referring next to FIGS. 1 and 2, there will be described how the lightdistribution characteristic change along the axis of the discharge arctube 2, i.e. in the longitudinal direction of the discharge arc tube 2.

FIG. 1 shows a state of the maximum convergence corresponding to FIG. 3,i.e. the state in which the light guide member 4 and the optical member5 are located at the maximum distance. FIG. 2 shows a state of thewidest illumination range corresponding to FIG. 4, i.e. the state inwhich the light guide member 4 and the optical member 5 are located atthe minimum interval. In these figures, elements and parts similar tothose described above are denoted by the same reference numerals, andthese figures also show the typical luminous fluxes in order to explainthe light distribution characteristicin the transverse direction.

First, there will be described the state shown in FIG. 1. As shown inthe figure, no refracting plane such as a Fresnel lens for use inconvergence is formed on the exit surfaces at the right and left of theoptical member 5. This is because the width of an opening formed in thelateral direction of the optical member 5 is narrower than the effectivearc length of the discharge arc tube 2 and there is only a shortinterval between the optical member 5 and the discharge arc tube 2. Morespecifically, if a sufficient distance cannot be ensured between thedischarge arc tube 2 and the exit side of the optical member 5 locatedat the maximum distance apart from the light source, it is difficult toconverge light since the angle at which the light source is seen fromeach point is excessively wide, even if any convergence plane is formedin the vicinity of the center.

For example, if a Fresnel lens is formed at the center of the opticalmember 5, luminous fluxes emitted from the center of the discharge arctube 2 and its proximity can be converged, whereas luminous fluxesemitted from the ends of the discharge arc tube 2 cannot besatisfactorily converged since there is the high possibility that theillumination range is widened by refraction, the loss of light is causedby unexpected reflection resulting from the total reflection, and theloss of light is caused by refraction at the edge of the Fresnel lens.For this reason, lateral luminous fluxes are not converged at the exitside of the optical member 5 according to the present embodiment.

On the other hand, prism sections 5 h, 5 h′ that are comprised ofentrance surfaces 5 e, 5 e′, total reflection surfaces 5 d, 5 d′, andexit surfaces 5 f, 5 f′ are formed at the periphery of the opticalmember 5 at a side toward the light source. The prism sections 5 h, 5 h′converge only lateral luminous fluxes. The reason why the prism sections5 h, 5 h′ are formed only at the periphery of the optical member 5 isthat the angle at which the light source is seen from the periphery isnarrower than at the center, the direction in which the light source isseen from the periphery can be limited to some degree, so that thedirections of luminous fluxes can be controlled to some degree.

Therefore, according to the present embodiment, the shapes of therespective surfaces of the prism sections 5 h, 5 h′ are optimized so asto achieve the maximum convergence as shown in FIG. 1. As shown in thefigure, luminous fluxes incident upon the prism sections 5 h, 5 h′ amongluminous fluxes emitted from the vicinity of the right and left and thecenter of the light source are totally reflected to be made parallelwith the exit optical axis.

Referring next to FIG. 2, there will now be described the widestillumination range in the transverse direction. It should be noted thatFIG. 2 also shows luminous fluxes emitted in the same direction from thesame point of the light source so that it can be compared with FIG. 1.

As stated above, no special refracting plane or reflecting plane forconverging lateral luminous fluxes is formed at the exit side of theoptical member 5. Thus, luminous fluxes incident upon a flat entrancesection 5 g are distributed uniformly over the wide range withoutnarrowing the illumination angle in the transverse direction.

In further detail, as is clear from FIG. 2 showing the rays of lightemitted from the center of the light source and its vicinity, if thelight guide member 4 and the optical member 5 are arranged close to eachother, all the rays of light emitted from the light guide member 4 canenter the flat incidence section 5 g of the optical member 5. Thisprevents any component from entering the prism sections 5 h, 5 h′ andachieves a light distribution characteristic with a wide illuminationrange.

Referring next to FIG. 7, there will be described how the illuminationrange changes in the state shown in FIGS. 1 and 2.

In FIG. 7, the abscissa represents the angle with respect to the center,and the ordinate represents the quantity of light with respect to theangle. Here, character G indicates the convergence corresponding to thestate in FIG. 1. In this state, the effective illumination range isequal to a range of angle A in which the quantity of light is equal to50% of the quantity of light at the center.

On the other hand, symbol H indicates the wide illumination rangecorresponding to the state in FIG. 2, and the effective illuminationrange is equal to a range of angle B.

As is apparent from these figures, the convergence shown by symbol Gindicates that the effective illumination range regulated to be 50% ofthe central quantity of light is relatively narrowed as a result of theincrease in the quantity of light in the vicinity of the center byconverging a part of luminous fluxes radiated toward the periphery, inthe center and its vicinity.

Thus, if luminous fluxes emitted in such a direction as to go fartherfrom the center of the exit axis (toward the left and right longitudinalends of the optical member 5) among luminous fluxes emitted from thelight guide member 4 enter the prism sections 5 h, 5 h′ provided at theright and left of the optical member 5 to change the directions of theluminous fluxes in converging directions, the quantity of light in thevicinity of the center can be significantly increased and the quantityof light radiated outside of a required illumination range is reduced.This enables the efficient radiation of illumination lightcorrespondingly to the long focal length of the taking lens.

On the other hand, if the optical system is arranged in the intermediatestate between the state in FIG. 1 and the state in FIG. 2, theillumination range of illuminating luminous fluxes can be variedcontinuously by changing the relative positions of the light guidemember 4 and the optical member 5. This is because the quantity ofluminous fluxes directed to the center of the exit optical axis and itsvicinity can be changed continuously according to the quantity ofluminous fluxes incident upon the prism sections 5 h, 5 h′ formed in theoptical member 5 (the quantity of luminous fluxes reflected by the totalreflection surfaces 5 d, 5 d′) and that the effective illumination rangein which the quantity of light is regulated to be 50% of the quantity oflight in the vicinity of the center can be changed continuously byincreasing or decreasing the luminous fluxes in the vicinity of thecenter.

More specifically, the quantity of light incident upon the prismsections 5 h, 5 h′ is gradually increased from the state in FIG. 2, andthis changes the direction of the luminous fluxes emitted toward theperiphery so that the luminous fluxes can be directed to the vicinity ofthe center of the exit optical axis. It is therefore possible tocontinuously narrow the illumination range.

Although the respective surfaces of the prism sections 5 h, 5 h′ areshaped so that the luminous fluxes emitted from the center of the lightsource can be totally reflected by the prism sections 5 h, 5 h′ andemitted along the exit optical axis. It should be understood, however,that there is no intention to limit the present invention to it. Forexample, the respective planes of the prism sections 5 h, 5 h′ may beshaped so that luminous fluxes emitted from the intermediate positionbetween the center and periphery of the light source can be concentratedin the vicinity of the exit optical axis by the optical member 5.Alternatively, the respective reflection surfaces of the prism sections5 h, 5 h′ may be shaped arbitrarily so that preferable lightdistribution characteristics can be achieved at respective zoomingpoints in view of an intermediate point of movement.

Thus, the optical system is able to change the illumination range in thetransverse direction correspondingly to the change in the illuminationrange in the vertical direction shown in FIGS. 3 and 4. Morespecifically, a single action, that is, the relative movement of theoptical unit and the optical member 5 along the exit optical axisenables a change in the illumination range in both vertical andtransverse directions. This realizes an optical system with variableillumination range, which is very convenient because there is no needfor an interlocking system and the illumination angle can be changedwidely.

Further, since the total reflection surfaces 5 d, 5 d′ are used tochange the optical paths at the periphery in the lateral direction andthe prism sections 5 h, 5 h′ are formed to cover the both end portionsof the exit surface of the light guide member in the longitudinaldirection thereof, the illumination range can be changed efficientlywith little loss of light caused by the change in the direction.

Further, according to the present embodiment, the illumination range inthe transverse direction is changed by using the control planes (totalreflection surfaces 5 d, 5 d′) different from the light control planesthat are used to change the illumination range in the verticaldirection. Therefore, the illumination range can be changed separatelyin the transverse and vertical directions, and can be set freely in thetransverse and vertical directions.

Although the above description is made by referring to the case wherethe reflection surfaces include the prism sections 5 h, 5 h′ integratedwith the optical member 5 are used as means for changing theillumination range in the transverse direction, but it is possible touse reflection surfaces such as bright aluminum integrated with theoptical member or prism members provided separately from the opticalmember.

According to the present embodiment, the illumination range is changedby moving the converging section relative to the light source along theexit axis, but it should be understood that there is no intention tolimit the present invention to it. The same effects can be achieved byarbitrarily controlling the directions of incident luminous fluxes byusing an optical member that is capable of significantly changing theexit directions of the incident luminous fluxes (e.g. an optical fiberand a gradient index material with variable refractive index within thesame member).

FIGS. 8 to 13 show the optical arrangement of an illuminating deviceaccording to a second embodiment of the present invention. The presentembodiment is different from the first embodiment in that the directionof relative movement of a light guide member 24 and an optical member 25in changing the illumination range is reversed. More specifically,according to the present embodiment, the illumination range is widenedto the utmost limit when the light guide member 24 and the opticalmember 25 are located at the maximum interval, and the illuminationrange is narrowed to the utmost limit when the light guide member 24 andthe optical member 25 are located at the minimum interval. That is,luminous flux components emitted toward the outside of a requiredillumination range in FIG. 8 are utilized as peripheral componentswithin a required angle of view to thus substantially widen theillumination range.

In the description of the present embodiment, elements and parts similarto those of the first embodiment are denoted by the same referencenumerals. The illuminating device according to the present embodiment isalso mounted in a camera as described with respect to the firstembodiment.

FIGS. 10 and 11 are vertical longitudinal sectional views showing thecenter of the discharge arc tube 2 and its vicinity, and are also tracedrawings showing the illuminating luminous fluxes emitted from thecenter of the discharge arc tube 2 and its vicinity. FIG. 12 is aperspective view showing essential parts of an illumination opticalsystem according to the present embodiment. FIGS. 8 and 9 are sectionalviews showing the discharge arc tube 2 taken along the axis thereof, andthey also show the typical light rays emitted from the center of thelight source and its vicinity.

Referring to FIG. 12, a detailed description will now be given ofcomponents that specify the optical characteristics of the illuminatingdevice according to the present embodiment.

In FIG. 12, reference numeral 23 denotes a reflection umbrella thatreflects components, emitted backward in a light exit direction, forwardin the light exit direction among luminous fluxes emitted from thedischarge arc tube 2. The inner surface of the reflection umbrella 23 ismade of a metallic material such as bright aluminum having a highreflectance. Incidentally, a metal having a high reflectance may bedeposited on the inner surface.

Reference numeral 24 denotes a light guide member that divides theluminous fluxes emitted from the discharge arc tube 2 into luminousfluxes in some optical path regions, emits the luminous fluxes in therespective regions from an exit surface thereof, and then causes theluminous fluxes to intersect at predetermined intervals to to change thelight distribution characteristic so that the luminous fluxes can bedistributed in a predetermined range.

Reference numeral 25 denotes an optical member that receives theluminous fluxes emitted from the light-permeable light guide member 24to achieve a predetermined light distribution characteristic. Aplurality of cylindrical lenses 25 a, which have a negative refractingpower to act in the vertical direction, are formed in parallel in thevertical direction on an entrance surface of the optical member 5.

Vertically extending prism sections (converging sections) 25 b, 25 b′that totally reflect incident light are formed at the right and leftperipheries of the optical member 25.

With this arrangement, the discharge arc tube 2, the reflection umbrella23 and the light guide member 24 are integrally held in a holding case,not shown, to constitute an emission unit. The emission unit is movedrelative to the optical member 25 fixed on the external surface of theilluminating device. This continuously changes the degree of convergenceof illumination light. It should be noted that the light guide member 24and the optical member 25 are preferably made of a resin material foroptical use with a high light transmittance such as acryl resin or aglass material.

According to the present embodiment, if a zoom lens is used as a takinglens of the camera, the relative positions of the light guide member 24and the optical member 25 along the axis of illumination light arevaried according to the focal length of the zoom lens. This enables thelight distribution characteristic in the vertical direction to changecorrespondingly to the angle of view of the taking lens, and enables thelight distribution characteristic in the transverse direction, in whichluminous fluxes are essentially difficult to control due to theexcessively large size of the effective light source, to changecorrespondingly to the angle of view of the taking lens without usingany other members.

There will now be described the method of setting the optimum opticalarrangement for changing the illumination range with reference to FIGS.8 to 11.

FIGS. 10 and 11 are vertical longitudinal sectional views showing thedischarge arc tube 2 in the diametric direction thereof in theilluminating device according to the present embodiment to describe thebasic principle of changing the illumination range in the verticaldirection. In these figures, elements and parts similar to thosedescribed with reference to FIG. 12 are denoted by the same referencenumerals. FIG. 10 shows the state in which the light guide member 24 andthe optical member 25 are located at the minimum interval, and FIG. 11shows the state in which the light guide member 24 and the opticalmember 5 are located at the maximum interval. FIGS. 10 and 11 also showoptical paths of light emitted from the center of the inner diameter ofthe discharge arc tube 2.

According to the present embodiment, it is possible to continuouslychange the illumination range while maintaining the uniform lightdistribution characteristic in the vertical direction, and a verticalopening is formed to have the minimum height.

First, there will be sequentially described the characteristics of theoptical system that is constructed as described above described. Theinner surface of the reflection umbrella 23 is semicylindrical andsubstantially concentric with the discharge arc tube 2 for the samereasons as in the first embodiment.

On the other hand, the upper and lower peripheries of the reflectionumbrella 23 are formed along the back of the light guide member 24 forthe reasons stated below.

Luminous fluxes emitted from the center of the light source are ideallyreflected by reflection surfaces 24 c, 24 c′ formed on the inner surfaceof the light guide member 24 as shown in the figures, but luminousfluxes emitted from the right side of the center of the light source inthe figures are partially emitted from the reflection surfaces 24 c, 24c′ particularly if the light source has a large inner diameter. Theupper and lower peripheries of the reflection umbrella 23 are shaped tocover the back of the light guide member 24 in order to effectivelyutilize such luminous fluxes emitted from the reflection surfaces 24 c,24 c′. More specifically, the reflection umbrella 23 is extended to theback of the light guide member 24, and is formed correspondingly to theshapes of the reflection surfaces 24 c, 24 c′. This enables the luminousfluxes, which are emitted from the reflection surfaces 24 c, 24 c′without being reflected by the reflection surfaces 24 c, 24 c′, to enteragain the light guide member 24. Therefore, the reflected luminousfluxes can be converged efficiently in a predetermined illuminationrange.

According to the present embodiment, the light guide member 24 is shapedas described below.

In the central section of the light guide member 24 in the verticaldirection, a cylindrical lens is formed on the entrance surface 24 a toprovide a positive refracting power, so that luminous fluxes emittedfrom the center of the light source can be made parallel with the exitoptical axis.

Likewise, in the upper and lower sections of the light guide member 24,luminous fluxes emitted from the center of the light source arerefracted by the entrance surfaces 24 b, 24 b′ and are reflected by thetotal reflection surfaces 24 c, 24 c′ located at the upper and lowersides of the entrance surfaces 24 b, 24 b′ so that the luminous fluxescan be made parallel with the exit optical axis.

After the luminous fluxes emitted from the center of the light sourceare once made parallel with the exit optical axis in the above-mentionedmanner, a plurality of cylindrical lenses 24 c having a positiverefracting power formed on the exit surface 24 d forms a plurality ofconvergence areas as shown in FIG. 11.

On the other hand, a plurality of cylindrical lenses 25 a, which havesuch a negative refracting power as to offset the power of thecylindrical lenses 24 d formed on the exit surface of the light guidemember 24, are formed on the entrance surface of the optical member 25.

With this arrangement, the refracting power of the cylindrical lenses isoffset when the light guide member 24 and the optical member 25 areclose to each other as shown in FIG. 10. This maintains the convergencestate in which the luminous fluxes are reflected by the reflectionsurfaces 24 c, 24 c′ after they are refracted by the entrance surface 24a of the light guide member 24 or refracted by the entrance surfaces 24b, 24 b′.

On the other hand, when the light guide member 24 and the optical member25 are located at the maximum interval as shown in FIG. 11, the lightdistribution characteristics can be changed so that the luminous fluxescan be distributed uniformly in a predetermined range. This is becausethe luminous fluxes of the respective sections converged by thecylindrical lens 24 d of the light guide member 24 are transmittedthrough the center of the cylindrical lens 25 a and its vicinity with alow refracting power in the optical member 25. Such arrangement of theoptical system reduces the effect produced by the cylindrical lens 25 aon the luminous fluxes.

Moreover, when the optical system is arranged in the intermediate statebetween the state in FIG. 10 and FIG. 12, it is possible to continuouslychange the effect produced by the refracting power of the cylindricallens 25 a with movement of the light guide member 24, i.e. change in thedistance thereof relative to the optical system. Therefore, the lightdistribution characteristics can also be changed according to change inthe distance of the light guide member 24. By regulating the relativepositions of the light guide member 24 and the optical system, it ispossible to continuously and uniformly change the light-distributioncharacteristics.

Thus, it is possible to continuously change the light distributioncharacteristic in the vertical direction according to change in therelative positions of the light guide member 24 and the optical member25 along the exit optical axis.

Referring next to FIGS. 8 and 9, there will be described a change in thelight distribution characteristic in the transverse direction. Thesefigures are horizontal longitudinal sectional views including a centralaxis of the discharge arc tube 2. FIG. 8 shows the narrowestillumination range corresponding to FIG. 10, i.e. the state in which thelight guide member 24 and the optical member 25 are located at theminimum interval. FIG. 10 shows the widest illumination rangecorresponding to FIG. 11, i.e. the state in which the light guide member24 and the optical member 25 are located at the maximum interval. Inthese figures, elements and parts similar to those described above aredenoted by the same reference numerals, and these figures also show thetypical luminous fluxes emitted from the center of the light source inorder to explain the light distribution characteristic in the transversedirection.

As illustrated in the figures, the exit surfaces at the right and leftperipheries of the optical member 25 are designed to be flat for thesame reasons as in the first embodiment. Specifically, since the opticalmember 25 is close to the light source and the light source is longerthan the opening in the optical member 25, it is difficult to convergelight since the angle at which the light source is seen from each pointis excessively wide even if any convergence plane is formed.

On the other hand, prism sections 25 b, 25 b′ that converge only lateralluminous fluxes are formed at the right and left peripheries of theoptical member 25.

The reason why the prism sections 25 b, 25 b′ are formed only at theright and left peripheries of the optical member 25 is that the angle atwhich the light source is seen from the periphery is narrower than atthe center and the direction in which the light source is seen from theperiphery is limited to some degree, so that the directions of luminousfluxes can be controlled to a certain extent.

As is apparent from the trace drawing, the luminous fluxes emitted fromthe center of the light source cannot be converged in the state shown inFIG. 8, and the same rays of light as those emitted form the center ofthe light source in FIG. 8 enter the prism sections 25 b, 25 b′ so thatthe rays of light are deflected into a predetermined exit direction.

This will now be described in further detail. The prism sections 25 b,25 b′ are comprised of flat entrance surfaces 25 c, 25 c′; asphericaltotal reflection surfaces 25 d, 25 d′; and the right and leftperipheries of a flat exit surface 25 e.

As is apparent from the trace drawing of FIG. 9, the entrance surfaces25 c, 25 c′ are flat so that they can be substantially vertical to theexit optical axis in order to increase the quantity of incidence lightand minimize the size thereof.

The total reflection surfaces 25 d, 25 d′ are aspherical and extendvertically, i.e. perpendicularly to the plane of the figure so that theluminous fluxes emitted from the exit surface 25 e can be reflected at apredetermined angle θ.

The illumination angle in the lateral direction can be widened by apredetermined degree by forming the prism sections 25 b, 25 b′ in theabove-mentioned manner. The principle of changing the illumination anglein the state shown in FIGS. 8 and 9 will now be described with referenceto FIG. 13.

In FIG. 13, the abscissa represents the angle with respect to thecenter, and the ordinate represents the quantity of light with respectto the angle. Here, character I indicates the convergence correspondingto the state of FIG. 8. In this state, the effective illumination rangeis equal to a range of angle B in which the quantity of light is equalto 50% of the quantity of light at the center. In this state, theluminous fluxes at the right and left peripheries cannot be utilizedeffectively.

On the other hand, character J indicates the wide illumination rangecorresponding to the state of FIG. 9, in which the effectiveillumination range is equal to a range of angle C. As is apparent fromthe figure, the character I indicates the state in which theillumination range is widened by directing a part of luminous fluxes,radiated toward the right and left peripheries, to the periphery of arequired illumination range so that the quantity of light at theperiphery can be equal to about 50% of the quantity of light at thecenter.

Thus, the luminous fluxes that may be controlled by the prism sections25 b, 25 b′ can be used for changing the effective illumination range inthe illumination optical system that widens only the angular componentswithin a narrow area in which the quantity of light is equal to 50% ofthe quantity of light at the center since it is possible to quitecorrectly control the direction in which the rays of light (although theabsolute quantity thereof is small) emitted from a small gap with therelative movement of the light guide member 24 and the optical member25.

This method reduces the quantity of light radiated outside of a requiredillumination range to enable the efficient adjustment of theillumination range corresponding to the focal length of the taking lens.

According to the present embodiment, all the luminous fluxes emittedfrom the center of the light source are deflected at the predeterminedangle θ by the prism sections 25 b, 25 b′, but there is no intention tolimit the invention to it. For example, in the prism sections, thereflection surfaces may be arbitrarily shaped insofar as the quantity oflight in the vicinity of the periphery of the required illuminationrange can be increased. The same effects as in the present embodimentcan be achieved by optimizing the shape of the reflection surfaces.

Further, according to the present embodiment, a straight discharge arctube is used as the light source, but such discharge arc tube should notnecessarily be used as the light source. It is possible to use a lightsource (e.g. cold-cathode tube) that has an effective light emittingpart that extends to such a degree that the light source cannot beregarded as a point light source.

FIGS. 14 and 15 show the optical arrangement of an illuminating deviceaccording to a third embodiment of the present invention. The presentembodiment is different from the first embodiment in the shape of a partof an optical member 35. In particular, the present embodiment ischaracterized in that the respective prism sections provided at theright and left peripheries of the optical member 35 are divided into aplurality of parts to form prism rows.

In the description of the present embodiment, elements and parts similarto those of the first embodiment are denoted by the same referencenumerals. The illuminating device according to the present embodiment isalso mounted in a camera as described with respect to the firstembodiment.

Further, the illumination range in the vertical direction, i.e. in thediametric direction of the discharge arc tube 2 is changed in the samemanner as in FIGS. 3 and 4.

In FIGS. 14 and 15, reference numeral 34 denotes a light guide memberwhich luminous fluxes emitted from the discharge arc tube 2 enter andwhich changes the light distribution characteristics so that theluminous fluxes can be distributed in a predetermined range. Referencenumeral 25 denotes an optical member which the luminous fluxes emittedfrom the light guide member 34 enter to achieve a predetermined lightdistribution characteristic. Prism rows comprised of prism sections 35b, 35 c, 35 b′, 35 c′ are formed at the right and left sides of the exitsurface of the optical member 35.

FIG. 14 shows the state in which the illumination range is narrowed tothe utmost limit by arranging the light guide member 34 and the opticalmember 35 at the maximum interval, and FIG. 15 shows the state in whichthe illumination range is widened to the utmost limit by arranging thelight guide member 34 and the optical member 35 at the minimum interval.FIGS. 14 and 15 also show the traces of typical luminous fluxes emittedfrom the center of the discharge arc tube 2 and its vicinity. It shouldbe noted that the discharge arc tube 2 and the reflection umbrella 3 arethe same as in the first embodiment.

The convergence in the vertical direction in the state shown in FIG. 14is the same as in the first embodiment shown in FIG. 3. The convergencein the vertical direction in the state shown in FIG. 15 is the same asin the first embodiment shown in FIG. 4.

There will now be described the operation of the illuminating deviceaccording to the present embodiment. In the state shown in FIG. 14,among luminous fluxes emitted from the center of the discharge arc tube2 and its vicinity, the luminous fluxes incident on the prism rows 35 b,35 b′, 35 c, 35 c′, which are formed at both ends of the optical member35 in such positions as to face the light source, are deflected by totalreflection surfaces of the prism rows 35 b, 35 b′, 35 c, 35 c′. Thisincreases the luminous fluxes going toward the exit optical axis. It istherefore possible to increase the quantity of light at the center to alarger extent than in the case where the total reflection surfaces areformed to be flat.

According to the present embodiment, the illuminating luminous fluxesemitted from the light guide member 34 are refracted for convergence byreflection by a plurality of prism rows, which are formed at the rightand left ends of the optical member 35 in such positions to face thelight source optical and extend in the vertical direction, i.e.perpendicularly to the plane of the figures. Thus, even with thearrangement that the prism section is divided into a plurality of parts,substantially the same convergence effects can be achieved as in thefirst embodiment shown in FIG. 1.

In the state of FIG. 15, the luminous fluxes emitted from the lightguide member 34 immediately enter the optical member 35 without passingthe prism sections 35 b, 35 b′, 35 c, 35 c′ formed at the right and leftperipheries. Therefore, the luminous fluxes emitted form the dischargearc tube 2 from the same exit point and in the same exit direction asthe rays of light shown in FIG. 14 are not converged. This achieves alight distribution characteristic in which the luminous fluxes aredistributed in a wide range.

Although the prism sections are formed in two rows at the right side andtwo rows at the left side as reflecting sections that cause the opticalmember 35 to converge the luminous fluxes, but there is no intention tolimit the invention to it. For example, the prism sections may be formedin three or more rows. Moreover, the transverse area of the opening maybe increased to reduce the degree of projection of prism sections sothat they can be more flat.

Further, the prism section controls the illuminating direction by makingthe luminous fluxes emitted from the center of the light source parallelto the exit optical axis when the light guide member 34 and the opticalmember 35 are positioned apart at the maximum distance. It should beunderstood, however, that there is no intention to limit the inventionto it. The same effects as those of the present embodiment can beachieved insofar as the prism section is capable of capturing theluminous fluxes flowing toward the right and left peripheries and makingthem closer to the exit optical axis when the light guide member and theoptical member are apart from each other.

Further, according to the present embodiment, the prism rows formed onthe exit surface of the optical member 35 extend in the directionvertical or perpendicular to the plane of the figures, but there is nointention to limit the invention to it.

For example, it is possible to use prism rows that are inclined at apredetermined angle or orbicular prism rows that are concentric with oneanother.

FIGS. 16 and 17 show the optical arrangement of an illuminating deviceaccording to a fourth embodiment of the present. The present embodimentis different from the first embodiment that an optical member 45 ispartially modified differently from the third embodiment. In particular,the present embodiment is characterized in that reflecting members 46(reflecting boards 46), which are formed of separate members from theoptical member 45, are attached integrally to the right and leftperipheries of the optical member 45.

In the description of the present embodiment, elements and parts similarto those in the first embodiment are denoted by the same referencenumerals. The illuminating device of the present embodiment is alsomounted in a camera as described with respect to the first embodiment.

The illumination range in the vertical direction, i.e. in the diametricdirection of the discharge arc tube 2 is changed in the same manner asin FIGS. 3 and 4.

In FIGS. 16 and 17, reference numeral 44 denotes a light guide memberwhich luminous fluxes emitted from the discharge arc tube 2 enter andwhich changes the light distribution characteristics so that theluminous fluxes can be distributed along a predetermined width.Reference numeral 45 denotes an optical member which the luminous fluxesemitted from the light guide member enter to achieve a predeterminedlight distribution characteristic. Reference numerals 46, 46′ denotereflecting boards attached integrally to the optical member 45.

FIG. 16 shows a state in which the illumination range is narrowed to theutmost limit by arranging the light guide member 44 and the opticalmember 45 at the minimum interval, and FIG. 17 shows a state in whichthe illumination range is widened to the utmost limit by arranging thelight guide member 44 and the optical member 45 at the maximum interval.FIGS. 16 and 17 also show the traces of typical luminous fluxes emittedfrom the center of the discharge arc tube 2 and its vicinity. It shouldbe noted that the discharge arc tube 2 and the reflection umbrella 3 arethe same as in the first embodiment.

In the state shown in FIG. 16, the convergence of luminous fluxes in thevertical direction is the same as in the first embodiment shown in FIG.3. In the state shown in FIG. 17, the convergence of luminous fluxes inthe vertical direction is the same as in the first embodiment shown inFIG. 4.

There will now be described the operation of the illuminating deviceaccording to the present embodiment. In the state shown in FIG. 16,among luminous fluxes emitted from the center of the discharge arc tube2 and its vicinity, the luminous fluxes incident on the reflectionboards 46, 46′, which are attached to both ends of the optical member 34in such positions as to face the light source, are deflected byreflection surfaces formed as aspherical curved surfaces on thereflecting boards 46, 46′. This increases the luminous flux componentsflowing toward the exit optical axis. It is therefore possible toincrease the quantity of light at the center to a larger extent than inthe case where the total reflection surfaces are formed in flat planes.

According to the present embodiment, the illuminating luminous fluxesemitted from the light guide member 44 are refracted for convergence byreflection by the reflecting boards 46, 46′, which are provided at theright and left ends of the optical member 45 in such a manner as to factthe light source and extend in the vertical direction which isperpendicular to the plane of the figures. Thus, by using the reflectingmembers, substantially the same convergence effects can be achieved asin the first embodiment shown in FIG. 1.

In the state of FIG. 17, the luminous fluxes emitted from the lightguide member 44 immediately enter the optical member 45 without passingthe reflecting boards 46, 46′ provided at the right and leftperipheries. Therefore, the luminous fluxes emitted form the dischargearc tube 2 in the same exit direction from the same exit point as therays of light shown in FIG. 16 are not converged. This achieves a lightdistribution characteristic in which the luminous fluxes are distributedin a wide range.

According to the present embodiment, aspherical reflecting curvedsurfaces extending in the vertical direction which is perpendicular tothe plane of the figures are formed on the reflecting members that causethe optical member to converge the luminous fluxes, so that the luminousfluxes emitted from the center of the light source are deflected tobecome parallel with the exit optical axis. It should be understood,however, that there is no intention to limit the shape of the reflectingmembers to the above-mentioned shape. The same effects as in the presentembodiment can be achieved insofar as the reflection boards are shapedsuch that they are capable of capturing the luminous fluxes flowingtoward the right and left peripheries and making them closer to the exitoptical axis when the light guide member and the optical member areapart from each other.

According to the present embodiment, the reflecting members are used tocapture the luminous fluxes radiated through a gap between the lightguide member 44 and the second optical member 45 toward the side tochange the illuminating direction. This achieves substantially the sameeffects as in the embodiments described previously except that theluminous fluxes falling upon the right and left peripheries of theoptical member 45 directly from the light guide member 44 cannot becontrolled and hence a part of the rays of light cannot be utilizedeffectively and that the quantity of light may be reduced according tothe reflectance of the reflecting members. As is the case with theembodiments described previously, the present embodiment enables thecapture of luminous fluxes that cannot be utilized in the prior art andtherefore makes it possible to efficiently control the lightdistribution characteristics.

According to the present embodiment, the reflecting boards 46, 46′ fixedto the optical member 45 are shaped so as to extend in the verticaldirection, i.e. perpendicularly to the plane of the figures, but thereis no intention to limit the shape of the reflecting boards to theabove-mentioned shape. The reflecting boards 46, 46′ may be formed asflat surfaces, spherical surfaces, rotary ellipsoids, or the like. It ispossible to efficiently change the illumination range by optimizing theshape of the reflecting boards 46, 46′.

According to the embodiments described above, the illuminating device ismounted in a camera using a film, but the illuminating device of thepresent invention may also be mounted in a variety of photographingapparatuses such as digital still cameras and video cameras. Moreover,the present invention may be applied not only to the illuminating devicewhich is a built-in type installed in a photographing apparatusaccording to the above described embodiments, but also to an externaltype illuminating device. Further, the present invention may be appliedto an illuminating device for use in optical communication using strobelight.

As described above, according to the embodiments described above, thelight source unit (emission unit) and the optical member are movedrelative to one another to increase or decrease the luminous fluxcomponents reflected by the reflecting sections toward the both ends ofthe optical member among the fluxes of illumination light emitted fromthe light source unit are increased or decreased to thus change therange of illumination by the fluxes of illumination light. This realizesan illuminating device that is capable of suitably controlling theillumination range in the longitudinal direction of the light sourceunit with a simple and compact structure. It is therefore possible toreduce the size and weight of a photographing apparatus in which theilluminating device is mounted, and to improve the photographingperformance of the photographing apparatus.

Further, since the illumination range is changed by increasing ordecreasing the luminous flux components reflected by the reflectingsections, the illumination range can easily be changed continuously bycontinuously increasing or decreasing the luminous flux components.

Further, since the reflecting sections are arranged in such positions asto cover the end portions of the exit surface of the emission unit andthe total reflection surfaces are used as the reflecting sections, theenergy from the light source unit can be utilized efficiently.

Moreover, since the optical member is provided with an optical operationpart that moves the light source unit and the optical unit relative toone another so as to change the range of illumination by the fluxes ofillumination light in a different direction (e.g. a directionperpendicular to the longitudinal direction of the light source unit)from a direction (the longitudinal direction of the light source unit)in which the illumination range is changed by increasing or decreasingthe emitted luminous fluxes components reflected by the reflectingsections, it is possible to realize an illuminating device that iscapable of properly controlling the illumination ranges in both of theabove-mentioned directions with a simple and compact structure withoutthe need for a mechanism that changes the illumination rangescorrelatively in both of the above-mentioned directions, or the like.

It should be noted that if the reflecting sections are providedseparately from the optical operation part, it is possible to change theillumination ranges separately in the above-mentioned directions and toraise the degree of freedom in setting the illumination range in anydirection.

It should be understood, however, that there is no intention to limitthe invention to the specific forms disclosed, but on the contrary, theinvention is to cover all modifications, alternate constructions andequivalents falling within the spirit and scope of the invention asexpressed in the appended claims.

1. A light emitting device comprising: an emission unit including atleast an arc tube; and a pair of reflecting means arranged in thelongitudinal direction of said arc tube, for reflecting luminous fluxesemitted from said arc tube in a direction which varies according to adistance between said emission unit and each of said reflecting means,wherein the luminous fluxes emitted from said arc tube do not reach saidreflecting means when the distance between said emission unit and eachof said reflecting means is shorter than a predetermined distance, andthe luminous fluxes emitted from said arc tube reach said reflectingmeans when the distance between said emission unit and each of saidreflecting means is longer than the predetermined distance.
 2. A lightemitting device comprising: an emission unit including at least an arctube; and a pair of reflecting means arranged in the longitudinaldirection of said arc tube, for reflecting luminous fluxes emitted fromsaid arc tube in a direction which varies according to a distancebetween said emission unit and each of said reflecting means, whereinsaid emission unit comprises a light guide member for guiding luminousfluxes emitted from said arc tube in a predetermined direction, saidlight guide member being disposed to lie between said pair of reflectingmeans when the distance between said emission unit and each of saidreflecting means is shortest.